Patients with low renin essential hypertension (LREH) have an exaggerated ratio of plasma or urinary aldosterone to plasma renin activity while taking an unrestricted sodium diet or during volume contraction with furosemide or dietary sodium restriction. We have tested the hypothesis that this abnormal aldosterone/renin ratio in LREH results from an increased sensitivity of the adrenal receptor for aldosterone synthesis to angiotensin II (AII) by administering A II intravenously to 20 normal volunteers and 24 patients with low (9) or normal (15) renin hypertension. Patients with LREH have greater increases in plasma aldosterone concentrations and diastolic blood pressure per unit of A II infused than do normal volunteers or patients with normal renin essential hypertension. This adrenal supersensitivity to A II is not compatible with a primary adrenal defect causing LREH.